1. Field of the Invention
The present invention is related to an imaging apparatus such as a digital camera. More specifically, the present invention is related to an imaging apparatus and an imaging method that utilizes an imaging element equipped with two types of light receiving elements, which are capable of being controlled and driven independently from each other.
2. Description of the Related Art
CCD's, which are imaging means employed in digital cameras, have narrower dynamic ranges than silver salt film. Therefore, overexposure and underexposure are likely to occur in images photographed by digital cameras. For this reason, various imaging techniques for obtaining image data sets having expanded dynamic ranges have been proposed. A first example of such an imaging technique is that in which a plurality of image data sets which have been obtained under different exposure conditions are combined. A second example of such an imaging technique is that in which a CCD, constituted by an arrangement of main pixels (first light receiving elements) having high sensitivities and sub pixels (second light receiving elements) having smaller areas than the main pixels and therefore lower sensitivities but are less likely to be saturated, is utilized. In this technique, high sensitivity image data obtained by the main pixels and low sensitivity image data obtained by the sub pixels are combined, to obtain a combined image data set that exhibits favorable reproduction properties over a wide range from high brightness to low brightness.
U.S. Patent Application Publication No. 20070223059 discloses an imaging apparatus that utilizes the aforementioned second technique. This imaging apparatus switches the process by which image signals are processed based on a dynamic range prioritizing drive mode, a resolution prioritizing drive mode, a sensitivity prioritizing drive mode, a color reproduction prioritizing drive mode or the like, which is selected by a user or selected according to scenes. Japanese Unexamined Patent Publication No. 2006-148591 also discloses an imaging apparatus that utilizes the aforementioned second technique. This imaging apparatus switches the drive method of the two types of CCD's according to subject field scenes.
In addition to providing different light receiving areas, changing the exposure times of light receiving elements is another technique for imparting sensitivity differences among light receiving elements.
In the imaging apparatuses described above, the drive mode is determined for each scene. Therefore, the image signal processing method and the CCD drive method are determined simultaneously with discrimination of a scene.
There are two general types of scenes which are discriminated. The first is a subject field scene (subject field data) such as the brightness of a subject and color temperature. The second is a subject scene, such as scenery, portrait, and night scene. If the image processing method and the CCD drive method is determined only on the discrimination results of the subject field scene, if the brightness and the color temperature of subjects are the same value, that is, if the results of discrimination of the subject field scene are the same, the same image signal processing method and the same CCD drive method are used regardless of whether the subject scene is a portrait or scenery. Accordingly, the obtained image may not be an optimal image of the subject. Similarly, if the image signal processing method and the CCD drive method are determined based only on the discrimination results of the subject scene, the obtained image may not be an optimal image of the subject.